Automatic amplitude balancing circuits



Sept. 1, 1953 w. P. FRANTZ 2,651,033

AUTOMATIC AMPLITUDE BALANCING CIRCUITS Filed Jan. 2l, 1952 5 Sheets-Sheet 1 Mia/w T005 Sept. l 1953 Fil ed Jan. 21, 1952 W. P. FRANTZ AUTOMATIC AMPLITUDE BALANCING CIRCUITS 5 Sheets-Sheet 3 20,000//5 'vl VL -H @I300/ls LV J1 TM-f INVENTOR W/BERT P. FRA/viz ATTORNEY Sept l, 1953 W, P, FRAN-rz 2,651,033

AUTOMATIC AMPLITUDE BALANCING CIRCUITS l Filed Jan. 21; 1952 5 sheets-'sheet 4 nam/mwa mm1/way @ONT/m www0/ws Wagggs' sept. 1, 1953 w. P. FRANTZ AUTOMATIC AMPLITUDE BALANCING CIRCUITS 5 Sheets-'Sheet 5 Filed Jan. 21, 1952 INVENTOR W/L 19E/e7 P. FRANTZ f/Y #w ATTRNEY Patented Sept. l, 19.53

2,65igt33 were AMBLITUDE Meer@ rIfhis invention relates. to, automatic amplitude halancingcreuits and especially Vto automail. pulse amplitude balancing circuits. useable in hyperbolic navigation receivers.

1n a hyderbolie navigation system a pair oi. spacel` ground stations transmit. radio signals synchronously in all directions. 'These signals travel through space with the velocity of. light, arriving lat a remote receiving station afterlan elapsed time interval equal to the distance Qctween the 'ground station and the receiving. station divideil bythe velocity of light. At the Te.- ceiving station' the difference in time between the arrival of a first signal from 'one of. the ground stations and the arrival of the'signal from the. other ground station is accurately measured. The locis of all points inspace at which thetime difference linterval' between arrivals of signals from the spaced ground stations are equal form an imaginaryV cnrveexpre'ssecl mathematically as a"spheric`al 'hyprbo'lafwherein the foci of the hyperbola are the two spaced ground stations.. For each different time diererce interval bet'vveen the 'arrivals ofthe signals from the two. spaced'grounz stations, Ithere exists a' diierent hypeloola. @ver the surface ofthe earth these, different hyprbias formA a fainnyof aecratmy established unes off position. 'From other pairs of spaced ground stations at different locations, additional families oi hyperbolic lines of position are established. Th`e`irit`e'rseotion of a specific hyperbolic 'lineA ofposition tronone pair of stationstth as'peeiiie hyperbolic line :of position fro?. another pair of statoins establishes a nay.: gati'oii'afl.' l@ne Well `lgnown hyperbolic navigation system is the'Loran'system"'1n' the Loran system one gron'd'st' onflnoiim as the master,"tran'sm'ts lperiojiic fpulses of" accurately established reeurrenee intem'al`s`,r for example 25 pulses per second. A The second ground'station, "known`a`s the yslave.tran'sim"ts' periodic "Bl pulses oi the samereeurrence interi/alas the master pulses but'delayedtime', 'The cliiratiimr of.` the Vtransf initted andBp'ulses is approximately 4;() microsc'les Thee paises transmitted from the slave are aocuratelydelaye. in tiinefromthe A pulses transmitted from the'master by 'an amount equal tomthe'r'alio travel time iromthe master to the. slave," piusone-half the recurrence' interyal oi the pulses, plus a Yfired time delay known as the eigf iei'a'y. "ffrhs, the time interval from the piiwingo'the mastrtofthepulsing of theslave "ays'greater'than onelhaltth plse recurinterval; "This" pulsing Vsequenceproizides of the Loran pulses to.

cathoderar msm with the. separation talige@ is applis@ @9. the. Y?. @am eotion plates, of the cath cie-ray indioator alo4 j pulseY prende@ wllcil ap ear 0n th the indicator, during the, s dition. The first or A pedestal appears sta onary Qn the, upper trate ata need an@ po after, tnestart oi the sweep 1.111@ l@ edge of the trace. efiiastagle lay; circuits Qontrol the. peileil Qf lh? .@C'f orf-B. pedestal., appears .an te? lQWiiafJ by. acurately. @ated time dlelylfiifal's layed from the. start Qi ih e Reti the slow. sweepzspeee t, frequency of the. @mille 9i small amount relatiye Q 15h..

Leren pulses as viewed the Qflfe 1 eater., in order to position the Laren A` r' aloe of the A pedestal. thereafter, there non frequency. of the timing i. muy maintained in smantellare with. @12e Leren pulses by automatic smclirfmiziag emits? ile''c'* by holdmefhe' A puise atop of the A aeclesia The adjustable B pedestal positional by. the precisintimedelayeiregitsalongthe, so as vroeien/ale the Loran B. pulse atop Q1" i?.Y pedestal. me reeei ine @naar l the time :inference i al between the i3 and B pulses is facilitated by medium and fast sweep-speed voltages in the following manner'. A medium sweep-speed voltage is derived from the A and B pedestals and initiates the upper trace coincident with the start of the A pedestal and initiates the lower trace coincident with the start of the B pedestal, the time duration of the sweeps being identical to the time duration of the pedestals. The A and B pulses on their respective traces are magnified in width and can be aligned accurately one above the other. The A pulse remains in its stationary position on the upper trace as before while the B pulse now can be shifted to the right or left by advancing or delaying the starting time of the sweep voltage under the control of the precision time delay circuits. To facilitate a more precise alignment or match of the A and B pulses, a fast sweepspeed voltage is produced in the same manner as above and the trace separation voltage is removed from the cathode-ray indicator thereby bringing together the expanded A and B pulses onto a single trace. The B pulse now is shifted under the control of the precision time delay circuits so as to appear directly coincident with the A pulse to form a perfect match of the leading edges of the two pulses. Since the received Loran pulses from the nearer Loran station are the stronger, in forming a perfect match it is necessary that the A and B pulses be made to have the same amplitude and an amplitude balancing circuit is provided for this purpose. The precise time delay interval between the A and B pulses is read directly from the counter in the precision time delay circuits. A comprehensive treatment of the Loran system may be found in the book Loran edited by Pierce, McKenzie, and Woodward and published by the McGraw-Hill Book Co., 1948.

The services of a trained operator are required to manipulate the numerous controls of a Loran navigation receiver-indicator to obtain useful navigational information. The accuracy of the information obtained is dependent upon both the skill and speed of the operator in matching the A and B pulses to obtain a Loran reading. Accordingly, the accuracy of Loran readings is improved by simplifying and reducing the manual adjustments necessary to match trie received A and B pulses and by providing automatic controls whenever possible. Heretofore the operator in making the iinal precise match of the expanded A and B pulses on the face of the Loran indicator manipulated a manual amplitude balance control to maintain the amplitude of the A and B pulses of equal value, a manual gain control to set the Loran pulses at a suitable constant peak value, and a manual time delay control to maintain the leading edges of thc A and B pulses precisely coincident. The present invention provides a system of amplitude balance and gain control which is accomplished automatically thereby relieving the operator of two manual operations and affording an improvement in the il? maintaining the amplitude of one voltage wave equal in value to the amplitude of a corresponding voltage wave.

A more specific object of the invention is to provide in a hyperbolic navigation receiver simplied apparatus for automatically maintaining the amplitudes of the output master and slave pulses of equal value.

Another object of the invention is to provide in a hyperbolic navigation receiver simplified apparatus for automatically maintaining the amplitudes of the output master and slave pulses at a selected constant value.

Yet another object of the invention is to provide an improved hyperbolic navigation receiver with a minimum of manual controls to thereby reduce the time necessary for a navigator to obtain a navigational fix.

The above brief description and objects of the present invention will be more fully understood and further objects and advantages will become apparent from a careful study of the following detailed description in connection with the drawings, wherein,

Fig. 1 is a block diagram of a Loran receiverindicator illustrating the automatic amplitude balance of this invention,

Fig. 2 is a detailed block diagram of the receiver of Fig. 1,

Fig. 3 shows the waveforms of voltages associated with the Loran receiver-indicator of Fig. l,

Fig. 4 shows the waveforms of voltages associated with the automatic synchronizing circuits and the automatic amplitude balancing circuits of Fig. 1,

Fig. 5 is a schematic diagram of the amplitude balancing circuits of the invention, and

Figs. 6a, 6b, and .6c are views of the delineations on the face of the cathode-ray indicator showing the alignment of the Loran pulses for three successive sweep speeds.

In the several figures of the drawings, similar reference numerals refer to similar parts. The illustrated waveforms of the voltages or currents associated with the various individual blocks are identified in the block diagrams by capital letters associated with the lead or leads carrying the voltages or currents.

RECEIVER Referring to Fig. 1, the Loran A and B pulses from remote master and slave stations are collected by antenna II and supplied to the input of superheterodyne receiver I2. Referring particularly to the detailed block diagram of receiver I2 in Fig. 2, antenna coupling unit I3 matches the impedance of antenna I I to a threeposition step attenuator I4 providing xed amounts of attenuation in steps of 0, 20, and 40 decibels respectively. Radio frequency amplifier I5, mixer I6, and local oscillator Il are in accordance with conventional superheterodyne practice. Channel switch S-5 selects one of four receiving frequencies Within the standard Loran band. Conventional I. F. amplifiers I8 and detector I9 amplify and detect the heterodyned Loran pulse signals and supply detected negative A and B pulses to interference reducer 20. Interference I' reducer 20 is a resistance-capacitance differentiating circuit and when switched into operation by S-I reduces the effect of certain forms of interference, namely continuous wave radio signals. While introducing a characteristic distortion, the interference reducer does not affect the accuracy of time difference measurement since both A and B pulses are distorted in exactly the same manner. Video amplifier 2l supples positive A and B pulses over lead 22 in Fig. 1 to the operations terminal of test switch S-2 and over lead 23 to the input of the A. F. C. amplifier IIS. An automatic gain control voltage is supplied from an A. G. C. circuit, to be described later, to the gain controlling electrodes of the F. amplifiers i8 and mixer l5. Amplitude balance restorer 24 supplies an automatic amplitude balancing control voltage to the gain controlling electrode of R. F. amplifier l5. Description of the amplitude balance restorer 24 appears hereinafter in connection with the automatic amplitude balancing circuits.

PRECISION TIlWIN G CIRCUITS The precision timing circuits comprising the oscillator and divider circuits, the square-wave circuits, the A delay circuits, and the B delay circuits are similar to those described and claimed in application S. N. 633,473 led December '7, 1945 in the name of Winslow Palmer, entitled Timing Apparatus and assigned to the same assignee as the present invention. These circuits are the same as employed in the DBE Loran receiverindicator shown and described in the aforementioned book Loran on pages 358 through 363.

Oscillator and divider circuits The conventional oscillator and divider circuits of block 25, Fig. 1, comprise a crystal-controlled oscillator operating at a frequency of 100 kilocycles per second, and a cascade of ve frequency dividers, dividing the frequency of the oscillator output voltage in the steps of 5, 4, 5, 5, and 4 respectively, followed by a transient delay circuit. These circuits supply the basic timing voltages of the Loran receiver-indicator. The output voltage from the first frequency divider is supplied over lead 35 to one input of the B delay circuits 65 and over lead 3l to one input of the A pedestal synchronizer 58. The output voltage from the third frequency divider is supplied over lead '35 to one input of the A pedestal delay 51 and over lead 36 to a second input of the B delay circuits. The output voltage from the fourth frequency divider is supplied over lead 39 to a third input of the B delay circuits and the output voltage from the transient delay circuit, illustrated'as waveform C of Fig. 3, is coupled over lead 50 to the input of the square-wave circuits and over lead 52 to the sweep circuits 106.

The basic pulse repetition rates used in Loran are 331/3, 25, and 20 cycles per second and are identified by the letters H, L, and S. These pulse repetition rates are provided in the oscillatordivider circuits 25 by the basic P. R. R. switch S-8A coupled over lead i0 to the fifth frequency divider. This switch S-SA controls the frequency division of the fifth frequency divider to provide a division of 3 for the rate H, 4 for the rate L, and 5 for the rate S. In addition to the three basic pulse repetition rates H, L, or S, seven additional specific pulse repetition rates identified as 0 through '7 are employed in Loran. The specific P. R. R. switch S- controls the feedback of pulses from the output of the fth frequency divider to the inputs of the second and third frequency dividers to provide these specific rates in the oscillator-divider circuits 25.

A reactance tube circuit 4S is coupled to the 100 kilocycle-per-second crystal oscillator and corrects the frequency of this oscillator in fre- Ispouse to a negative automatic synchronizing or delay 57 and A pedestal synchronizer 58.

automatic frequency control voltage supplied over lead 49 from the A. F. C. circuits. A description of these circuits will appear hereinafter.

Square-wave circuits Fig. 3, whose frequency equals one-half the repetition frequency of the trigger pulses. The frequency of this square-Wave voltage corresponds to the pulse repetition rate of the Loran signals. The mark and space time intervals of the squarewave voltage are identical and equal to 20,000 microseconds for rate LO. The square-wave voltage is coupled to a push-pull cathode follower 53.

Cathode follower 53 produces push-pull squarewave output voltages, one voltage inverted in phase with respect to the other. One of these square-wave voltages is supplied over lead 54 to the input of the A delay circuits 55 and to the B delay circuits 50. The other square-wave voltage is supplied over lead 5B to the arm of operations switch S-3C. Both of the square-wave voltages are supplied to the amplitude balancing circuit l25 of this invention. The negative portion of the square-wave voltage over lead 5d energzes the A delay circuits 55 and is eventually synchronized ,so as to be the time interval during which the A pulses from 4the master station arrive at the receiver-indicator. The positive portion of the square-wave voltage over lead 54 energizes the B delay circuits 60 and is the time interval during which B pulses from the slave station arrive at the receiver-indicator.

A delay circuits The A delay circuits 55 comprise a pedestal The A pedestal delay 5l is in Eccles-Jordan circuit with a differentiating circuit (not shown) at each of its two inp-uts. The square-wave voltage of waveform D on lead 5d is differentiated by one of the differentiating circuits to produce negative trigger pulses coincident with the trailing or negative going edges of the square-Wave voltage. These negative trigger pulses initiate the A pedestal delay. rThe voltage on lead 35 from ythe third frequency divider with a recurrence interval of 1000 microseconds is dierentiated by the other differentiating circuit to produce negative trigger pulses of 1000 microseconds recurrence interval coincident with the trailing edges of the voltage. The A pedestal delay 5l is terminated by the rst of the 1000 microsecond negative trigger pulses following the initiation of the A pedestal delay. The output from A pedestal delay 51 is a series of positive pulses of 1000 microseconds duration, illustrated as waveform E in Fig. 3, and whose recurrence interval equals the recurrence interval of the square-wave voltage from cathode follower 53.

Both positive and negative pulses from the A pedestal delay are applied to the left-right 'switch f fer-1A. .The vpositive 'zpulsesfare :coupled through" the leftposition. of` switcht'S-'IA through :position 1l of'isWitch.S-L3Ftothe1 input of the third frequency divider over lead 41. rThe function of the posi-tive-'pulsesxon lead 4l is to delay the triggering of the third frequency dividerby one more -of ts200 microsecorid input "pulsesand thus increasethe recurrence interval -of the Ioutput pulses from the'n'fth 'divider1by-2'0`0 microseconds. This increase vvin recurrence interval eventually results in an increase? 'inf theV recurrence interval ofthe-sweep Voltage-applied -to the cathode-ray indicator. Thel'sweep recurrence interval When longer lthanf-Tthe 'recurrence linterval -of the received'Loran `pulses causes' lthe ldelineatedA and'B pulses to drift-slowly'across the face -of 'the indicator to the left.

vNegative pulsesfrom-ftheiA pedestal: delayi vare coupled through -the "fri'gh y'position of switch S-l-A and through- 'position 1 Vfof' switch S-BF -to lead'4'i. The negative -pulseson lead/4l coupled to the input f the third frequency `divider perform the function of-pretriggering this ldivider by one' lessmf-` its`200 mi'crosecoridA` lpulses and thus reduce the recurrence-'interval ofA the output pulses from the fthdivider by`l200 "microseconds. This reduction in recurrence interval eventually 'resultsl .in 'ai reduction iin the recur- 'rence interval of vthe sweepvoltage applied tothe cathode-rayV indicator. -A'dshorterwsweep :recurrence interval ltlian-the'recurrenceinterval of received Loran pulsescauses Ythe delineated-A and VB pulses yto dri'ftlslovvly across thefaceofthe indicator tothe right. When the .flet-right switch 'S-'lvA-fis in fits= lneutral-rpositionf vthere .is

-no feedback of pulses from the'Af.pedestal delay Yl and consequently thereisnoddrift Aofthe delineated A and' B `pulses; thesweep recurrence interval now being equal tothe recurrence interval of the received :A and B pulses.

The A pedestal synchronizer f58 isf-falso 1an -Eccles-Jordan y'circuit Withz-a differentiating circuit (not shown) `at eachv ffits two inputterminals. The positive pulsesrom thefA pedestal `delay 5l are differentiatedby'one of the differentiating circuits tofor-'m-rnega'tive trigger `pulses coincident with the .trailing edges of the positive pulses. The negative'trigger -pulses initiate the A pedestal synchronizer 58. The voltage on lead -3i from the first frequency divider, with arecurrence interval of '50 microseconds,v is 'differentiated by the other diferentiatingcircuit to produce negative trigger v vpulses 'of 50 microseconds recurrence intervals coincident with the trailing edges of the'voltage. The A pedestalsynchronizer 58 is terminatedby the' first of the 50 trailing edges ofy these output pulses, Whose =delay time is less than one `microsecondjfis. under the accurate control offthe dmicrosecond recurrence interval output pulses on leads-.3| fromthe first frequency divider. .The Arecurrent output pulses from A pedestal synchronizer 58 are coupled over lead/5910 the input-.lof pedestal circuits 99.

5 "ofrrecurrence interval equal to the recurrence mtervaL-ofthe square-Wave voltage of Waveform Dlonzvleadellrandwhose time delay With respect .-to' the recurrent output pulses from the A delay circuits '55::is adjustable by accurately known '10 :famountsin'dicated -on 1a time difference counter 89. Ther-time delay-difference'between the out- :put;;pulses..fromfLtheA Idelay circuit -andthe B delaycircuitris established'wi-th an-accuracy better than one :'microsecond. The recurrent Variably delayed output pulses from Bfzdelay circuits 60 occur during the time interval that the square- Wave vbitage'on 'lead'-54"ispositive. *The recurxv'rentoutput.pulses from the' Adelaycircuits occur `:during-theY time interval that ,the square-wave g .voltagennflead 54-is negative. -A xed time delay -eXac-tly equal .to'one-:half ,the recurrence `interval of@ thessquarev-Wave' voltagefon lead 54 exists betweenthe recurrent ,pulses .from theB del-ay cir- .:cuitszlland. .the recurrent-pulses from the Aide- '.25 @lay circuitsnnin:addition ,to` the-variable time i.delayintroducedibyfthe.B delay circuits. y

:The-Bfdelaypircuits-as shown and ydescribed in :the :aforesaidzz-application S. N; 633,473 comprise coarse, medium and fine phase-shifting 1.30 channels. The rotationsffcoarse; medium and )fine-.phase -slfxiftingy transformers in Y these chan- ?nelscontrol= theV time vposition of the'` recurrent vmrtput. pulsesfromthe-.Bfdelay circuitson lead 1:88. =These-variably-.delayedrecurrent pulses of :g5-approximately. -30 .microseconds duration are .illustrated as iiwaveform G- -of Fig. V3. VThree Y,sinusoidali voltages for excitingthe three phaseeshiffting .transformersare-,.derived through ampliersand flow-pass Afilters .from the yappropriate f401vo'ltagesfon the -leads 30..-36,1and -39 from the .fre-

yquency dividers :ini the Aoscillator-divider circuits .25. The threephaseshiftingI transformers are .-,coupled through a'gear. train to time difference -counterqll tesa. fine delay controlknobSS, `and -ftona1motor. .The-.motor-v is energized-by `coarse delayl switch S3-9. :The gear ratiosbetween each ..vof the vxthree ,phase-shifting transformers are eequaletoethe ratios :oftheir frequencies and ro- ,.tation ofthe-gear train yunder the-.control of the :line .delay :knob 96hor .the motorvproduces. the

.- samef .time sdelay. in .V-al1.. three :channels :Three alphase-.shifted'sinusoidal-voltages :from.the three phase-shifting transformers :are squared I.and ...differentiated Ato .yield ,-.pulses that Aterminate ..-three.-mono.stable-or one-shot multivibrator type ,60- minated, ydepending on the -bias selected by -a range-extender; potentiometer, by the rst, second, orthird pulse .derived from the-output of thecoarse phase-shifting channel. The time de- ..lay provided by thel rstselector Amay be varied continuously sover the range Yof approximately 3770-to almost 20,000 .microseconds under the con- L trol of the fine delay knobV 95. The time delay so ,vprovided, however, is not vitself sufciently accurate for time ydifference measurements. Toobtain the precision'required,. the selecting process is repeated in two succeeding selectors of greater precision Whose output voltages are terminated r by output pulses -vfrom .the medium and fne -.phase-shifting channels. The second selectoris ,zadnitiated-.at-the termination ofthe first selector and is terminated by an output pulse from the medium phase-shifting channel. The third selector is initiated at the termination of the sec'- ond selector and is terminated by an output pulse from the i'lne phase-shifting channel, having the requiredprecision for accurate time difference measurements. The recurrent variably -delayed output pulses of waveform G from the B delay circuits 60 vary in time relative to the leading edges of the square-wave voltage of waveform D on lead 54 smoothly and unambiguously over the range of from 1050 to almost 20,000 microseconds. Moreover, the trailing edges of these variably delayed pulses vary in time relative to the trailing edges of the output pulses from the A pedestal synchronizer 58 on lead 59 smoothly and continuously over the range of exactly to almost 20,000 microseconds plus exactly one-half the recurrence time interval of the received Loran A and B pulses.

PEDESTAL CIRCUITS The pedestal circuit 99 comprises pulse mixer |00 and pedestal generator |0|. The positive recurrent output pulses of waveform F Fig. 3 from the A pedestal synchronizer 58 are supplied over lead 59 to one input of pulse mixer |00. The positive recurrent output pulses of waveform G Fig. 3 from the B delay circuits 60 are supplied over lead 88 to a second input of the pulse mixer |00. The pulse mixer |00 comprises a pair of grounded-grid amplifier stages with a common anode load resistance. Dierentiating circuits (not shown) at each of the two inputs to the pulse mixer |00 produce negative trigger pulses from the trailing edges of the respective positive recurrent pulses. The separate negative trigger pulses are combined across the common load resistance of mixer |00 and supplied to pedestal generator |0l. The negative trigger pulses from the mixer |00 appear as in waveform H Fig. 3.

Pedestal generator |0|, a mono-stable or oneshot multivibrator, is triggered on by each negative trigger pulse from mixer |00 and is terminated automatically by its own action as a monostable multivibrator. The pedestal generator is provided with two separate outputs, one supplying positive pedestal pulses and the other negative pedestal pulses. These output pedestal pulses are of 1300 microseconds duration for positions 1 and 2 of operations switch S-3B and of 175 microseconds duration for position 3. The positive pedestal output pulses are supplied over lead |02 to the arm of operations switch S-3C and also over lead |03 to terminals 2 and 3 of S-SA. These positive pedestal pulses appear as waveforms I and K of Fig. 3. The rst or fixed pedestal pulse is identiied as the A pedestal while the second or variably delayed pedestal pulse is identiiied as the B pedestal. The square-wave voltage from cathode follower 53 appearing on lead 55 is combined with the positive pedestal pulses on lead |02. These combined voltages appear as waveforms J and L of Fig. 3. The negative output pedestal pulses are supplied over lead 04 to terminals 2 and 3 of operations switch S-SE and also over lead |05 to the inputof the A. F. C. circuits H0. These negative pedestal pulses appear as waveforms O and Q of Fig. 3.

SWEEP CIRCUITS Sweep circuits |00 comprise a gate generator |01, a sweep generator |08 producing the slow. medium and fast sweep-speed voltages, and a sweep restorer |00. A dierentiatingcircuit (not shown) at lthe input to the gate generator |01 produces negative pulses from the trailing edges of the recurrent output Voltage from the oscillator-divider circuits 25 on lead 52. These negative pulses are amplified and inverted by the gate generator |01, a triode amplier, and supplied to terminal of operations switch S-3E. The positive pulses at terminal appear as waveform M of Fig. 3. These positive pulses are coupled to the input of the sweep generator |08 when the arm of switch S-3E is in position 1 and result in momentary conduction of the conventional triode sweep generator thereby discharging the .sweep condenser in parallel with the output of the triode tube. The sawtooth sweep voltage across the condenser, as shown by waveform N of Fig. 3, is applied to the input of horizontal sweep' amplier 2 of the cathoderay tube circuits With operations switch S-3 in position 2, the sweep generator |08 receives the recurrent negative pedestal pulses on lead |04 from pedestal generator 0| Sweep generator |08 produces a linear, medium sweep-speed voltage coincident with and for the duration of the recurrent negative pedestal pulses. This sweep voltage is illustrated as waveform P of Fig. 3 and the duration of the sweep voltage is 1300 microseconds. With operations switch S-3 in position 3, sweep generator |08 produces a linear, fast Sweep-speed voltage coincident with and for the duration of the recurrent negative pedestal pulses. For this position of switch S-S the sweep voltage is as illustrated by waveform R in Fig. 3 and is of 17.5 microseconds duration. Network ||0 coupling basic P. R. R. switch S-BB with switch S-3G functions to maintain the amplitudes of the three sweep voltages from sweep generator |08 of constant value for the three basic pulse repetition rates identied as H, L, or S. The sweep restorer |09, a diode D.-C. restorer, is coupled to the input of horizontal sweep ampliner ||2 and functions to clamp the lower edges of the three sweep voltages to a reference v oltage level. Sweep restorer |09 insures that the cathode-ray trace on the face of the cathode-ray indicator remains centered for each of the three sweep voltages and in addition insures that the horizontal sweep amplifier |2 operates over its linear transfer characteristic for each of the three sweep voltages.

vCATl-IODE-RAY TUBE INDICATOR CIRCUITS Horizontal sweep amplifier |2, a phase inverter amplier, supplies. push-pull sawtooth sweep voltages to the horizontal deflection plates of cathode-ray tube H3. Vertical amplifier H4, a phase inverter amplier, receives through the operations position of test switch S-2 the composite voltages comprising the pedestal and square-wave voltages of waveforms J and L of Fig. 3 and the received Loran A and B pulses from receiver I2. The vertical amplifier I4 supplies push-pull composite voltages to the vertical delection plates of cathode-ray tube I3. Intensity restorer ||5, a diode D.C. restorer, functions to blank the cathode-ray trace on the face of the cathode-ray tube 3 during the time intervals between sweeps on positions 2 and 3 of operations switch S-3. Positive pedestal voltages from pedestal generator I0! are supplied through positions 2 and 3 of switch S-3A to the input of the intensity restorer ||5. The restorer i|5 clamps the upper edges of the positive pedestal pulses to a reference voltage level corresponding to normal intensity of the cathode-ray trace on the face the pedestal pulsesfbeingenegative with'respeet tothe upper edges then .biasnthef control-,grid of. the `cathode-ray tube so as to blank the-cathode?. rayztrace.: Cathoderay:tube1 I'Siis supplied witlfii suitable 1 beam accelerating and: centering :voltages not shown. The delineations anpearingronfthe faceof the cathode-ray'tu'be II3 di'iting:..opera-v tion of. thereceiver-indicator are zas illustrated b'yi'lies. 6a; 6b, ande.- An' explanation ofthe operation of `the==receivereindicatorA to produce these delineations .willappear hereinafter.

AUTOMATIC. FREQUENCY.' CONTROL. CRCUITSII The automatic frequency, control circuits .I I6 alsov referred toas automa-tic:synchronizingp'cile cuits are -similarfftof :those described: and claimed in .application- Sv N. 74,218 rviileda February-2, ,1949; in tlriewnainev of WinslowPalnier entitled. Syn-. chronizer and assigned to ,thevamei-sglleefas the-present invention. The-YF. .C.,.crcil.iis H9 comprise` A. F. C.V delayf |I'|,- Ai.-.F. C.. ampliiier EIS. andA. F. C. synchroniser; H9,` Negative pedestal pulses of .waveformr-O or Qonlead|5 fromthe pedestal generator IBI aregsuppliedsto ya'differentiating circuit (no-tshown). at the input of the A.- E. C. delay I I'I. Negative trigger pulses resulting from diiierentiation o-f theleadingedges of the. negative., pedestal pulses initiate the A..F. C. .delay IIT, .af-.mono-,stable or one.sho.t multivibrator. The A.. F.- .C..delay is` automati-l cally terminated. approximatelyAv 100 microseconds after initiation by its owrninternal. action asia inonoestable multivibrator. The .output from. the A.. F. C..,delayv I llistak series of .recurrent negativey pulses of. 100 microseconds. duration. illus,- trated as waveform S. ot Fig,4 .4... These-1ecurrent negative pulsesy are. supplied to` .adierentiating circuit (notshown). at the. rstinput of A. F. C. synchronizer I I 9 and also .supplied .over lead .|21 tothe. automatic.. amplitude. balancing. circuits i26.,of this invention. Positivetriggerpulses, il# lustrated nas waveform T.. Fig.. 4 .resultingfrom difierentiation of .the trailingedges of .these-,Ilegative recurrent pulsesare appledto thefstim put .ofthe A..F. C. synchronizer I I9'.

Received vpositiver; .and .pulses Yfrom I.receiver i2 are applied over lead 23'tQ1713221119111;DALFICQ amplier IIS. Switch S-dplaces th'e A.' Ff C. circuits in operation.. The:Loranpulses-:arcaniplied and inverted.` by, ampler. .|.I 8 .a11d.t11e..out put .Loran pulses appear-as-wavefrmll of .Fisti- The negative output Loran'pulses aresllppli'edio a differentiating circuit (not'shown).` at .the second input of the A. F. Clsynchronizer |I9 .and also over lead |29' to the, automatic lamplitude balancing. circuits |26fof this invention. The output cf the A. F. C. amplifier ||8is grounded by left-right switch S'-'IB .whose arm is coupled over lead. |28 to the AJ. F'. C; amplifier. The A. F. C. operation is thus disabledduringithe left or rightpositions of 'switch S-I tovinsure proper. operation .of the left-.right drift' circuits.

The diierentiating circuit at; the second'inpugt of the A. F. C. synchronizer, I I 9 supplies differentiated A `and B pulses asillustrated lay-waveform V of Fig. 4 to the secondiinput ofiA. C. synchronizer IIS. The A; F.' C. synchronizer- I I9is a multi-gridY pulsel coincidenceV circuit producing recurrent output pulses of Lcurrentswhose amplitude varies according'tothe relativetimeposition or coincidence lbetween-the differentiated A pulse andthe particular-positive trigger-pulse I E5- and between'th'ef differentiated'-Be'pulse and the positive@trigger-pulse;,I llt.` The output 4pulses of currentifrom synchroniser. I I-S .are i applied to theel arma.f1-.1111er4 I 2|. i of. :polari.Zed-.-Y relay.- |22. The polarizedirela. I 2.2i: is energized :by: the-'squame waveevoltagcfiofwaveiorm D .Figi 4 Fwhich is ole tained.' from: .the relayrdriver -xI 3 I .off they automatic ga-irnbalancingr circuits I 2 6.1, The armature I 2 I vb'rates in: synchronismr wit-hy they square-.wave Voltage offiwaveformD and; separates thewoutput. pulsesffrom'; thepA';I C. synchronizer. I I 9 varying according; rtogtl'ietime .position o-f the: -diierentiated .iA-apulsesfirom the output pulses vary-l accordingrtoethe time position of vthe tinter-4 ent'iated .lpulsess The-.^sepa-1ated; .ouilpilt pulses Cl.Sy11..G,...Q1l..el-llnthatarewarying accor .nef-.to therr ativev time positio-nxof .the-,differentiated iA pulseswitht respect to the. positive trigger pulsessare.;-ap-1:liedI over; lead l |23 -to the longtime-constant ilter I 24 fwhere-'theyfaref in. tegrated to produce a negative D.C. controlvvolts age. The negative D.C. error control voltage on lead 49, illust-rated as waveform W of Fig. 4, biases react/.anne tuba-48 in: order toY maintain the frequencyfouthe 10.0 kilocycle-.per-,second loscillater 2:!5 suchf tha-tithepositivettigger pulses 4|45 into. theifrst inputiot A., F.- C. synchronizer II9 arelocked xirr,synchronismtothe. received dif.-I ferentiated A pulsesat the-secondinput to.A. F. C, synchroniser II9;-4 The.; aforesaid application yS: Ns '7452,18amay be-referred-to for additional details fof this .f-A.-

C. syst eine.

The magnitude. of.-. the. negativeU D.C. error control. voltageion leadV 49 isunder kthe independent manualgcontrolfof drift .potentiometer |25 andalef-t-fright ,sWitch-..S-.'LC coupled to. `lt.er,..|2|l. The -eleft-right-.swit.ch -S1.C..provides. two fixed negativecontrol voltages ot.different magnitudes from fliter.. I 25 .fonbiasing.reactanceY tube.48.. In the-lett .position ofswitch S-'IfC,..oneoi thesenegg atiye controlwoltages .causes the.delineated. Loran pulses to.Y drift islowly across theiaceof. .thecathodeeray tube ||3..to the leftwhile in theright p ositionthefother voltage causesY ahdriftof the delineated Apulses to ,therightA These two Voltages,-are.most;efectivedn, positions.. 2' and 3` of operatQnsSWitchgSa. the left-.right switch S-'IA being@ disconnecteddn thesepositions of switch Sp1-3F. The driftpotentiometer. |25 vprovidesan adjustable..negativecontrolV voltage from filter |24 .forslowly 'drifting the-delineated. A and .B pulses either tothe.. right or. theleft. These manual controls facilitatethealignment of the receivedngandj pulsesY atoptheir. respective A andB.. pedestals as heretofore described. Basic P.. R. R. swit`ch..Sf8.C coupled to lter |24 providesthree separate time constants for the filter corresponding lto the three `basic pulse Arepetition rates identifiedasI-I, L or S.

AUTOMATIC AMPLITUDE BALANCING CIRCUITS The automatic amplitudel balance controlpcircuits of this invention are shown as a block diagram IZBdnFig; 1 and also in circuit diagram form ,in Fig. 5. ReferringY to the block diagram |26, recurrent negative pulses illustrated as waveform Spf Fig. 4 are Supplied from A. F. C'. delay I I'I over lead |21 to a differentiating circuit (not shown) at-the first input to gain synchronizer |28. The' differentiating circuit produces positive pulses of approximately 5. microseconds duration, illustrated as waveform T of Fig. 4, from the trailing edges of the recurrent negative pulses of/Waveform- S and these positive pulses energize the'gain synchronizer. Negative Loran A and '.I?=-ffpulses,4 illustrated as--waveform- U'Fg. el,A are supplied from A. F. C. amplier ||8 to the second input of the gain synchronizer |28 over lead |29. The gain synchroniser |28 is a multi-grid pulse coincidence circuit producing recurrent output pulses of currentI whose amplitude varies according to the relative time position or coincidence between the particular microsecond positive pulse |45 of waveform T and the A pulse and between the particular 5 microsecond positive pulse |46 and the B pulse. The recurrent output pulses of current, also of 5 microseconds duration, from the gain synchronizer |28 are illustrated as waveform X of Fig. 4. Since the particular positive 5 microsecond pulse |45 has been made to occur at an instant that is coincident with the crossover of the diferentiated A pulse of waveform V by action of the A. F. C. system, it occurs at the instant corresponding to the peak of the A pulse of waveform U. Accordingly, the output pulse of current from the gain synchronizer |28 due to the coincidence of the positive pulse |45 and the A pulse varies according to the peak value of the A pulse. Moreover, the amplitude of this current pulse is inversely proportional to the peak value of the A pulse.

The particular 5 microsecond positive pulse |46 is brought into coincidence with the B pulse to produce an output current pulse from the gain synchronizer by the normal operating procedure of matching the received A and B pulses on the face of the cathode-ray tube ||3. The 5 microsecond pulse |46 is derived from the variably-delayed pulse of waveform S and the variably-delayed pulse of waveform S is derived from the B pedestal pulse. Therefore, the 5 microsecond positive pulse |46 is also a variably-delayed pulse. The time position of positive pulse |45 is under the control of coarse delay switch S-S and fine delay knob 96 of the B delay circuits 60. Accordingly, the output current pulse from the gain synchronizer corresponding to the positive pulse |46 varies according to the relative time diierence between positive pulse |46 and the B pulse. Moreover, the amplitude of this output current pulse is inversely proportional to the amplitude of the B pulse at the particular instant of the positive pulse |46. With the A and B pulses matched on the face of the cathode-ray tube |3, the relative time position between the positive pulse |46 and the B pulse is such that the positive pulse |46 is coincident with the peak value of the B pulse.

The output of the gain synchronizer |28 is coupled to the armature |30 of polarized relay |3|. The winding of polarized relay |3| is energized by the square-wave voltage of waveform D from the relay driver |32. The relay driver |32 is a push-pull power amplifier receiving the squarewave voltage from cathode follower 53. The armature |30 of relay |3| vibrates in synchronism with the square-wave voltage of waveform D to separate into different channels the output current pulses from the gain synchronizer |28 varying according to the amplitude of the A pulses from the output current pulses varying according to the amplitude of the B pulses. The current pulses varying according to the amplitude of the A pulses are supplied to low pass lter |33 while the current pulses varying according to the amplitude of the B pulses are supplied to low pass filter |34. Filter |33 integrates its input current pulses to produce a D.C. output control voltage of waveformY that is inversely proportional to the amplitude of the A pulses and lter |34 integrates its input current pulses to produce a D.C. output control voltage 14 of waveform Z that is inversely proportional to the amplitude of the B pulses.

Switch S-BD coupled to filters |33 and |34 provides three time constants for these filters for the three basic pulse repetition rates H, L, or S and supplies anode voltage to the multi-grid pulse coincidence tube. Control box |35 includes an automatic amplitude balance control on-oif switch |36, a manual gain control |31, and a manual amplitude balance control |38 and supplies appropriate control voltages to the input of cathode followers |39 and |40. With the automatic amplitude balance control ori-off switch |36 in the on position, the D.C. output control voltage from lter |33 is applied to the cathode follower |39 and the D.C. output control voltage from filter |34 is applied to the cathode follower |40. The D.C. output control voltages from the cathode followers |39 and |40 are applied to separate input of amplitude balance gate |4| and the D.C. control voltage from cathode follower |39is also applied to A. G. C. amplifier |42. The A. G. C. amplifier |42 amplies and inverts its D.C. input control voltage and supplies an A. G. C. voltage through cathode follower |43 to the control-grids of mixer I6 and I. F. amplifiers I8 of receiver 2. as waveform AA in Fig. 4. The A. G. C. voltage adjusts the gain of receiver I2 to maintain the amplitude of the ouput A pulses of suitable constant value, as the A. G. C. voltage is directly proportional only to the peak amplitude of the A pulses. Variations in the amplitude of the B pulses have no effect on the A. G. C. voltage.

The amplitude balance gate |4| is a balanced modulator comprising a pair of multi-grid tubes receiving two pairs of input voltages. control voltages from the cathode followers |39 and |40 form one pair of input voltages and the push-pull square-wave voltages of waveform D from cathode follower 53 form the other pair of input voltages. The amplitudebalance gate |4| produces a square-wave output voltage whose phase is determined by which of its two D.C. input voltages from cathode followers |39 and |40 is the larger and whose peak to peak amplitude varies according to the diiference between the two D.C. input voltages. This square-wave output voltage is either in phase with one of the push-pull square-wave voltages into the amplitude balance gate or the other. This squarewave voltage is illustrated as waveform BB of Fig. 4 and is known as the automatic amplitude balance control (A. A. B. C.) voltage.

The A. A. B- C. voltage is supplied through cathode follower |44 to amplitude balance restorer 24, a diode D.C. restorer, in receiver |2 which clamps the positive edge of the A. A. B. C. voltage to the A. G. C. voltage. As a result, the effect of the A. A. B. C. voltage is to reduce the receiver gain during negative portions of the A. A. B. C. voltage, the reduction in gain being relative to the gain control voltage. The A. G. C. voltage controls receiver gain during the reception of both A and B pulses while the A. A, B. C. voltage controls the receiver gain during the reception of only A pulses or B pulses but not both. For example, when the received B pulses are larger than the received A pulses as is the case in waveform U, the A. G. C. voltage sets the receiver gain such that the A pulses are of suitable constant amplitude as viewed on the face of the cathode-ray tube H3. 'The A. A. B. C. voltage reduces the receiver gain during reception of the B pulses until the amplitude of the B pulses as This A. G. C. voltage is illustrated' viewedfzon.:theiefacevoi the: cathode-ray, tube is" substantially the sameaamplitude asztheAfpulses:y

Forl the; case fwherel the :received'iApulsesmare largerfth'anu-thes received Bf..p.ulses, .then-phase. of

the; A... B: C. voltage is reversed 'and .bothi the-Y A." G. C'. voltage ancltheA.- A.' ByC. voltagefcontrolthe gain of. the .receiver during;` the. reception of 'the A pulses. The` gainfrof :the receiver is-re ducedsduringthereception of :the A. pulsesrel'a-y tive tothe Ygainduring;-receptiony .of :the 1BL pulses andzboth Af. G-.fC. andA. A; B. C.Yvo1tages set thegainr suchthat 'the Azpulses delineatedonV theface oiethecathode-rayv. tube-1 are f, of..y suitable constant. amplitude.'v Thef Bipulsesn are amplied more than: :the A pulses and:` the additionalv amountr :or amplication is such :that .tne delineated. Arand. Bfipulses Y,appearing-.onsthe lface ofthe cathoderayV tubev are substantially-y the same. amplitude: Inf: other fwords; the?. automaticamplitude balance controle action; is such that theastronger Loran pulse '.is'always :reduced in; amplitude with; outreducing `.the amplitude or the .weaker :Loran pulse;

Withuthe automatic amplitude lbalance control oneoff-'r switch- |362in theoi position, thef D.C.. control.l voltagesffronf1=.rl'ltersv |33 and |34- are shuntedzb'y -themanual gain control voltage-'andthemanualamplitude balance controll voltage renderingithe D-C. control'voltages fromv the lter ineiective.l The manual gai-rr control-|31 controlswreceiverI gain during thefreceptionof bothv AfandI B'. pulses and the manual amplitude balance controll 1| 38 controls freceiver gain during reception-fof'only Alpulses orfB pulses but notI both.;-

Fig, 'discloses thecircuit diagram of the automatic lamplitudebalancecircuits of theinvention.. The recurrent negative pulses of waveformV S-:fromfthe A. F; C. delayv I1 are coupled overlead I21`to :thediierentiatingcircuit comprising: coupling condenser I41and resistor |48. The -pulses of"5 `microseconds duration of waveform T resulting'from differentiation of the negative recurrentfpulsesare coupled to the controlgrid |49 of1the-multi'grid pulse coincidence tube |50# The pulse coincidence tube'l is normally cutoft inthe absence of the 5 microsecond input pulses-to the control-grid-MQ. The cathode |5| isata negative'potential with respect toy ground determined bythe voltagedivider comprising' resistors=|52and |53 coupled between a` source of negative-potential and ground. The control-grid l49f,however, is-at amore negative potential withv respect to ground. than the-.cathode |5I. The screen=grid-|54 is -at ground potential. During the occurrence 'of theI 5 microsecond, pulses on control-grid 149;'the tube I 5|! conducts and pulses of el'ectronsowrom cathode |5| to" anode |55. Th'eamount of the electron ow to the anode is determined .bythe'potenti'al existing Ion the third grid |56 Thepotential on this grid is normally thezsame` as on4 the cathode except during` the occurrence of received A- and B pulses. Negative rand B pulses from the A. F'. C. amplifier I I8 of waveformL U 'are coupled over lead |29 through coupling condenser |51 and resistor |58/tov the potentiometer attenuator 59. Attenuated` negative A 4and B pulses are supplied to the third grid |56wand' these negative pulses reduce the pulses of electrons.-that.floW Vin tube |50 when coincident with .the 5 microsecondv pulses on control-grid |49.' The momentary reduction'in the pulses'of electrons varies according to the amplitude of the negativezAandBpuisesfat the instants of the-5 microsecond,.pulses.Y Thegoutputsfrom.thesanode 554-is in: theiomn lofi-*currentpulses illustrated as Waveform; TheseJ current pulses.VY flow.A to armature Imhof-.relay |3I and. cit-her through 11e-.- sistor lvtothe-armfof: switch `S--D or through resistor IGI topthefarm of switchgS-tl. The'positive I' supply r.voltage at the :arxrr ofv switch :Si-.8D yis determined bygtheeswitch posi-tionH,l L, or S. and' thev resistor -voltagedividers 62', I 53, |64 `and I 65;.- Negative-.5 microsecond pulses proportionaltothe` amplitude of the current fpulses of 4waveforrrrX would. be produced .across :resistors I 6|) andA 6| if. 'it ywerenot for-'the integrating action off conV densers IEGf-and I|1intheilters |33 and 134.:- This integrating; action :produces instead a. D.C control voltagewacrossfthese resistors B, and |6f| which Variesl accordingto the-amplitude'pf the current pulses f of .waveformr.X-.. The =-D.C. conA trol voltage across resistor: I 6|? vis-.further smoothed: by-theintegrat-ing. action of'resistor |68-and condenserISS-'inthe filter |33 andtheD.-G. control- Voltage"across-resister I6! .isfurther smoothedeby` the'integratingfactioneofresistor |10 and con-V denser |1'I inthelterbl. The D.C.. control voltage'of lWaveform .Y fromlter I 33 is Supplied to the control-grid |12v-oftriodef |13whilethe- D.C-. controlnvoltagecf waveformf-,Z fromlter |34Ais supplied to;thecontrolgrid-|14of tube |15.-

The-polarized relays I 3 I `andV` 2 2 :are-energized by a square-wave. voltage` of-.waveform-D fromV the-relay driver comprising-.four triode-tubes |16;- I11, |18-and |19. Push-pull square-.Wavevo1t-A agefromicathode follower 53 is suppliedto the-in-l put of -thef relayv driver, one f-phase' of -thevpushpull. voltagebeing capacity-coupled .toI the controlgrids |89 4and-|83 of the triodes |16-.and |19; re spectively;y The-oppositeor inverted phase of the push-pull voltage'is.capacity-coupled to the control-grids |8| and |82. of the triodes |11and- |18,. respectively: Eachy of .thefour triode tubes con.- ducts `in ther absence ofinput square-wave -volt-` age since there` is nobiasvoltage-on the control-V grids kof `these` tubes.. Asi a result, thecommonterminal Sli-between thecathode of the tube |16 and theanode I -ofl tube` |11\isat the-same potential relative to ground as isthe potential existing at: thecommonY terminal' |31 between theZ cathode I88and :the anode |89. Thus, no )potentialexists r acrossl the'.V serially connectedwindings of thepolarizedf relays Y- |22 'and' |3|.- Upon` application of the vpush-pull square-wave voltage to 'thercontrolegrids of the tubes, thetubes |16v4 and |19'conduct-simultaneously during Vfthe half-'cycle that the squareewave voltage ontheir respectivecontrol-grids isf positive While at the same time-the tubes I11Ian'd" |18 are non-conducting since=fthesquare-wave: voltage' orr their control-'grids is'negative and these-latter two tubes-'are cutoff;V The potential atthecomrnon terminal |84 is raised while the `potential at the common terminali AI 81 islowered' and the winding of relays1|22iand= I3I are energized.n During this condition, current yiiows :from the common'connection |84 through the serially'connected Wind` ing-s of: th'e=relaysfin one direction to'thezcommon connection` |81. Both: of the armatures |2| land I 39 aren deected' so' vas to 'be positioned against one of their two contacts; Duringv the following half-cycle of the push-pullfsquarewave voltage to the relay; driver, the tubes :11B-.fand |19'are non-conducting `as thee Voltage onv their "respectiveIcontrol-grids isnegativezand these tubes Iare cut OIT -Whilew` at thezsamentime. thev tubesf |11 and' |18v are-.conducting as zthe-:Yvoltagea on .their respective-.fy controle-grids.: positive.; For.y this condition the potential at the common terminal |89 is lowered while the potential at the common terminal |01 is raised. Current now ows in the reverse direction from the common terminal |81 through the serially connected windings of the relays to the common terminal |34. Both of the armatures |2| and |30 are now deflected in opposite directions so as to be positioned against the other of their two contacts.

Of importance is the fact that the relay windings must be so serially connected and the pushpull square-wave input voltage applied to the relay driver be properly phased such that the armatures |2| and |30 of relays |22 and |3| switch their respective current pulses into the lters |24 and |33 during the reception of A pulses and armature |30 of relay |3| switches its current pulse into the filter |34 during the reception of B pulses.

With the automatic amplitude balance control on-off switch |35 of control box |35 in the 01T position, D.C. voltages under the manual control of the manual gain potentiometer |31 and the manual amplitude balance potentiometer |39 are supplied to the control-grids |12 and |14 of the triode tubes |13 and |15, respectively. The D.C. voltage to control-grid |12 is supplied through on-oi switch |36 from the arm of potentiometer |38 while the D.C. Voltage to the control grid list is supplied through on-oi switch |33 from the common junction between serially connected resistors |90 and |9|. The serially connected resistors |99 and |9| are coupled in parallel with the potentiometer |38 forming a bridge circuit. Negative supply voltage is coupled to the lower junction terminal of the bridge circuit through resistor |92 while positive supply voltage is coupled to the upper junction terminal of the bridge circuit through resistor |93 and manual gain potentiometer |31. In this 01T position of switch |36 the D.C. control voltages from the nit-ers |33 and |30 are shunted by the D.C. Voltages from the control box |35. Because the resistance values of the potentiometers |31 and |38 and the resistors |90 and |9| are chosen lower than the resistance of the resistors |60 and |558 of lter |33 and the resistors |6| and |10 of lter |39, the D.C. control voltages from the filters |33 and |34 are rendered ineiective. The manual amplitude balance control potentiometer |33 adjusts the D.C. voltage on the control-grid |12 relative to the D.C. voltage on the controlgrid |19. The manual gain control Potentiometer |31 raises or lowers the D.C. voltages on control-grids |12 and |13 together while having little effect upon the difference Voltage between these control-grids. A decreasing negative voltage on control-grid 12 produces an increasing negative manual gain control voltage.

With the automatic amplitude balance control on-off switch |36 in the on position, the D.C. voltage from the control box |35 is removed from control-grid |14 While the D.C, voltage on control-grid |12 is supplied from potentiometer |38 through resistor |94 of a high resistance value. The D.C. control voltages from the lters |33 and |39 are now eiectve. The purpose of the D.C. voltage coupled from the potentiometer |38 through the resistor |94 to control-grid |12 is to compensate for any unbalance in the tubes |13 and |19 as well as any unbalance in the tubes 20| and 202 of the amplitude balance gate.

The triodes tubes |13 and |14 operate as cathode followers and supply the output D.C. control voltage acrosstheir respective cathode resistors and |96 through resistors |91 and |98 to control-grids |99 and 200 of the multigrid tubes 20| and 202. The common junction between cathode resistors |95 and |90 is coupled to a negative supply voltage. The output D.C. control voltage across cathode resistor |95 is also supplied to the control-grid 203 of the triode vA. G. C. amplifier tube 209. Positive screen-grid voltage is supplied to the multi-grid tubes 29| and 232 through resistor 205. Positive anode yvoltage is supplied to tube 29| through anode load resistor 205 and to tube 292 through anode load resistor 201. The cathodes of the tubes 20| and 202 are coupled together and to a source of negative supply voltage through resistor 208. The push-pull square-Wave Voltage of waveform D from cathode follower 53 is supplied to the third grids 209 and 2 l of the multi-grid tubes through resistors 2|| and 2|2. Grid resistors 2|3 and 2|4 return these grids to a source of negative voltage. The square-wave output voltage across anode load resistor 205 and across anode load resistor 291 is coupled respectively through resistors 2|5 and 2|9 to the control-grid 2|1 of triode cathode follower 2|8. The automatic amplitude balance control (A. A. B. C.) voltage across the cathode resistor 2I9 of tube 2|8 is coupled through condenser 229 to the amplitude balance restorer 20 in receiver i2. The amplitude balance gate operates in the following manner. For the condition when the D.C. control voltage on the -controlgrid |99 of tube 20| is the same as the D.C. control voltage on the control-grid 299 of the tube 292, the magnitude of the amplified square-wave voltage across anode load resistor 295 is the same as across anode load resistor 21:1. However, since these output square-Wave voltages are exactly out oi phase, the difference between them appearing at the control-grid 2|1 is zero. Should the D.C. control voltage on control-grid |99 be more positive than the D.C.-control voltage on controlgrid 29|), then the amplication in tube 20| is larger than the amplification in tube 202 resulting 1n a larger square-wave voltage across anode load resistor 295 than across anode load resistor 201. The difference between these two out of phase output square-Wave voltages is no longer zero and there appears at the control-grid 2H a square-wave voltage whose peak to peak amplitude is equal to the diierence between the amplitudes of the two square-wave output voltages and whose phase is determined by the larger square-Wave voltage from tube 20|. Conversely, should the D.C. control voltage on the controlgrid 299 be positive relative to the D.C. control voltage on the control-grid |99, then the amplification or" tube 202 is the larger resulting in a larger square-Wave voltage across anode load resistor 291 than across anode resistor 206. The phase of the diierence square-wave voltage now appearing at the control-grid 2|1 is reversed, being determined by the larger square-wave voltage from tube 292. It is important that the pushpull square-wave voltage applied to the third grids 2r|9 and 2|0 be properly phased such that when the received A pulses are smaller in amplitude than the received B pulses, the A. A. B. C. voltage functions to reduce receiver gain during reception of the B pulses and not during reception of the A pulses.

The D.C. control voltage at the control-grid 203 of the A. G. C. amplifier is amplified and inverted by triode tube 204. The output voltage across anode load resistor 22| is coupled through a voltage dividercomprising resistors 222 and 223 19- to control-grid 224 of triode cathode follower 225. The A. G. C. voltage across the cathode resistor 221'6 is coupled to the mixer and I. F. amplifiers of receivers i2 as previously described.

OPERATION OF IMPROVE!) LQRAN RE- CEIVER-INDlCATOR Having described the improved Loran receiverindicator of this invention, it is believed worthwhile to conclude this specification with a more detailed description of the operation of the receiver-indicator to insure a complete understanding of the invention. The receiver-indicator is used in conjunction with suitable Loran charts of the area in which navigational information is required. Referring to Figs. 6a, 6b, and 6c, three illustrations are disclosed of the delineations of the Loran A and B pulses as they appear on the face of the cathode-ray indicator H3 correspending to the three sweep speeds provided in this equipment. The delineations, as appear in Fig. 6a, are obtained in the following manner. With the equipment placed in operating condition the channel switch S-5 is positioned so as to receive A and B pulses from the most suitable Loran master and slave stations in the area. The Loran charts are consulted'in the selection of these stations. The pulse repetition rate of the chosen Loran stations is selected by the basic P. R, R. switch S`8 and the specific P. R. R. switch S-i. rIsest switch S-2 is set to its operations position while operations switch S-3 is set to position 1'. With the automatic balance control on-o switch 136 in the 01T position, the amplitude of the delineated A and By pulses is adjusted to a suitable level by the manual gain control E37 and the attenuator S-G; Should interference be received along with the A and B pulses, the interference switch S-IA may be switched on. The A and B pulses appear substantially stationary on the face of the cathode-ray tube in arbitrary positions. To position the A puise atop of the A pedestal as shown in Fig. 6a, the left-right switch 'Sv-T is positioned to the right or leit to drift the pulse appearing upon the upper trace either to the right or left so that it will ride up on top of the A pedestal. With one pulse atop the A pedestal, the second pulse should appear on the lower trace to the'right of the A pedestal for correct positioning. In this case, the pulse atop the A pedestal is the A pulse and the pulse on the lower trace is the B pulse. However, should the second pulse also appear on' the upper trace, then it is the B pulse whichl 'hasv been drifted to ride up on top of the A pedestal and the positioning of the pulses is D'QOIIect. The left-right switch S-T must be deflected until the pulses assume the correct position. Since the received B pulses always arrive at 'the receiver at times greater than one-half the pulse recurrence interval following the A pulses, the above positioning of the pulses provides a positiveidentificationbetween the received A and B pulses. Should the A pulse tend to drift `slowly ofi the top or the A pedestal, this drift can be stopped by adj'usting'the knob ofthe drift potentiometer |251 Once ythe rA pulse has been positioned atop the A pedestal 'near its left-hand edge, the A. F. C. switch kS-A is switched on. Automatic synchronization of the sweep voltage in the receiver-indicator to the pulse repetition rate of the received Loran pulses is established as previously explained in connection with the` A. F. C. circuits andthe A pulse remains fixed atop the A pedestal. The-slow sweep-speed voltagefor posi- Effi 20 tion 1 of operations switch S-3 is illustrated as waveform N.

The B pulse on the lower trace is elevated atop the B pedestal by positioning the B pedestal to the right or left with the coarse delay switch S-9. Coarse delay switch S-Q when positioned to the right or left energizes the motor in the B delay circuits to drive the geared phaseshifting transformers in the B delay circuits so as to vary the time delay of the B pedestal relative to the A pedestal. The motor drives the gear train at high speed so as to quickly Vposition the B pedestal. The counter 89 geared to the phaseshifting transformers revolves so as to indicate the amount of the time delay difference when the A and B pulses are correctly aligned.

Next, the operations switch S-S is set to position 2 and the delineated A and B pulses appear as in Fig. 6B. For this position of switch S-S it may be recalled that the sweep voltage producing the upper trace is initiated coincident with the leading edge of the A pedestal and the sweep voltage producing the lower trace is initiated coincident with the leading edge of the B pedestal. Moreover, the sweep-speed is increased as illustrated by the sweep voltage of the waveform P in order to expand the width of the delineated A and B pulses. For this condition, a change in the time delay of the B pedestal causes the delineated B pulse to be shifted to the right or left across the face of the cathode-ray tube in contrast with position 1 of operations switch S-3 above in which the B pedestal is shifted to the right or left while the B pulse remained stationary. The fine delay knob d5 is positioned now such that the B pulse `on the lower trace appears directly under the A pulse on the upper trace as illustrated in Fig. 6b. The automatic amplitude belancecontrol on-o switch |36 now may beset to its on position to automatically balance the amplitudes of the A and B pulses. Heretofore, the A and B pulses may have 1eeen different in amplitude or they may have been approximately balanced in amplitude by the manual amplitude balance control potentiometer 138. Nevertheless, with the automatic amplitude balance control on-off switch |36 in its on vposition and with the A and B pulses approximately matched, the amplitudes of the delineated A andy Bpulses hereafter will be automatically balanced to have substantially equal amplitudes.

Finally, operationsswitch S- is set to position 3 and the A and B pulses matched as shown in Fig. 6c so that their leading edges are precisely coincident. This final match requires only Athe adjustment of the ne delay control knob 9E. As observed in Fig. 6c, the trace separation voltage obtained from-cathode follower 53 has been removed thereby bringing together the tracesfone upon the other and `thesweep speed further-increased to expand the width of the delineated A and B pulses. The sweep Voltage for this condition is illustrated 'as-waveform The time difference interval whichfis the iLoran number is read directly from the counter SQ. ber corresponds to a Loran line ofV position and may be located on the Loran charts. To obtain a second Loran line of'-position, the entire above procedure must, be .repeated employing vLoran pulses` received from a second pair of Loranstations. The intersection of, the-second YLoran line of position with the iirstLoran line of position establishes anavgational fix which` is the .location of the LQran'recever-ndicator inspace.

lSince .many changes couldr be made ,in the- This 'num-- above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the a-ccompanying drawings shall be interprete-d as illustrative and not in a limiting sense.

What is claimed is:

1. In a hyperbolic navigation receiver receptive to master pulses and slave pulses from distant transmitters wherein the strength of the received master pulses may be different from the strength of the received slave pulses; an automatic amplitude balance control system comprising, means coupled to the output of said receiver and alternately producing a first voltage version varying according to the-strength of said master pulses and a second voltage version varying according to the strength of said slave pulses, means coupled to said producing means and separating said rst voltage versions and said second voltage Versions into diierent channels, means responsive to the difference between the strengths of the separated first and second voltage versions to produce a control voltage, and means` adjusting the amplification of said received master pulses and said received slave pulses with said control Voltage Yto produce output master and slave pulses of equal amplitude.

2. In a radio navigation receiver responsive to recurrent A pulses transmitted from a master station and to recurrent B pulses transmitted from a slave station, each of said recurrent B pulses arriving at the receiver at a time delayed from the arrival of each of corresponding recurrent A pulses; an automatic amplitude balance control system comprising, means coupled to the output of said receiver and alternately responsive to said recurrent A and B pulses to produce first recurrent output pulses varying according to the strength of said A pulses and second recurrent output pulses varying according to the strength of said B pulses, switching means coupled to the output of said responsive means for separating said first recurrent output pulses from said second recurrent output pulses, automatic gain control means responsive to said first recurrent output pulses and coupled to said receiver for adjusting the receiver gain to maintain the amplitude of said output A pulses of constant value, and means responsive to the difference between the amplitudes of said rst and second recurrent output pulses and coupled to said receiver for controlling the gain during the time interval of reception of one of said received recurrent pulses to maintain the amplitude of said output B pulses equal to the amplitude of said output A pulses.

3. In a hyperbolic radio navigation receiver responsive to recurrent A pulses transmitted from a distant master station and to recurrent B pulses transmitted from a distant slave station, each of said recurrent B pulses arriving at the receiver at a time delayed from the arrival of each of corresponding recurrent A pulses; an automatic amplitude balance control system comprising, synchronizer means coupled to the output of said receiver and alternately producing short output pulses varying according to the amplitudes of the received A pulses and the received B pulses, switching means coupled to said synchronizer means for separating into different channels the short output pulses varying according to the amplitude of the A pulses from the short output pulses varying according to the amplitude of the B pulses, iirst lter means coupled to said switching means and producing a first control voltage from the short output pulses varying according to the amplitude of the A pulses, second lter means coupled to said switching means nad producing a second control voltage from the short output pulses varying according to the amplitude of the B pulses, means coupling the first control voltage from said rst filter to said receiver for controlling the receiver gain to maintain the amplitude of the output A pulses of constant value, means coupled to the first and second filter means and producing a third control voltage responsive to the difference between the rst and second control voltages, and means coupling the third control voltage to said receiver for controlling the receiver gain during the reception of one of said recurrent pulses to maintain the amplitude of the output A and B pulses equal in value.

e. In a hyperbolic radio navigation receiver responsive to recurrent A pulses transmitted from a distant master station and to recurrent B pulses transmitted from a distant slave station, wherein the strength of the received recurrent A pulses may be diierent from the strength of the received recurrent B pulses, each of said recurrent B pulses arriving at the receiver at a time delayed from the arrival of each of corresponding recurrent A pulses; an automatic amplitude balance control system comprising, a rst pulse generating means producing recurrent output pulses of duration less than the duration of said recurrent A pulses, a first synchronizer means coupled to the output of said navigation receiver and synchronizing the recurrent output pulses from said rst pulse generating means with said recurrent A pulses, a second pulse generating means producing recurrent output pulses of duration less than the duration of' said recurrent B pulses and delayed in time rela-- tive to the recurrent pulses from said rst pulsegenerating means, means adjusting the time de lay of the recurrent output pulses from the sec-- ond pulse generating means to establish coin-- cidence with said recurrent B pulses, a secondi synchronizer means coupled to the output of.' said navigation receiver and responsive to the? coincidence of the said recurrent A pulses with the recurrent output pulses from the first pulse generating means and responsive to the coincidence of the said recurrent B pulses with the recurrent output pulses from the second pulse generating means, said second synchronizer .means producing recurrent output pulses varying according to the strengths of said recurrent A pulses and said recurrent B pulses, switching means coupled to the output of said second synchronizer means for separating into different channels the recurrent output pulses varying according to the strength of said recurrent A pulses from the recurrent output pulses varying according to the strength of said recurrent B pulses, first filter means coupled to said switching means and producing a first control voltage from the output pulses varying according to the strength of said A pulses, second lter means coupled to said switching means and producing a second control voltage from the output pulses varying according to the strength of said B pulses, means coupling the first control voltage from said rst filter to said receiver for controlling the receiver gain to maintain the amplitude of the recurrent output A pulses of constant value, means coupled to the output of the deemed first andssecond filter means and-.responsivetoz said rst and second controluvoltagesto.produce; a third. control voltage responsive to the difference between said rst and. secondl control. voltages and means couplingsaid' thrdcontrol voltage to said receiver for controlling thereceiver gain during the reception. of one-*of-.saidyreceived recurrent pulses to maintain the amplitudeof the recurrent output AL andzB pulsesequal in,

value.

5'. In a radio navigation receiver-a1ternatelyresponsive toa rst pulsey received duringa rst.

time interval and to a second pulse received during a second time interval Where-in. the .strength of the received first pulses may be derent from the strength 0I". the received second pulses, means coupled 'to the output ofl said receiver andproducing a. rsti control voltage according to the strength of. rsaid-rstpulse:and producing a second control voltage varying according to the strength of said second pulse, means coupled to said producing. means and responsive to said first-and second .controlfvoltages -for producing a thirdcontrolvoltage varying accordving to the relative strengths of said-rst and; second control voltages, andmeans'including a'.

coupling for-introducing` said ,third control .voltage into the navigationreceiver for controlling. they gain of the receiver during one ofthe time* intervals to maintain the amplitudes of the rst'.

and secondl output pulses equal in value.

6. An automatic pulse amplitude balancing :circuit comprising.. means alternately producing a :first pulse during a rst time intervalanda second .pulse during asecond time: intervaLi said means including .a controllable `transmission circuit transmitting. said first` and second'pulses,

means coupled to the outputof-said producing...

Ameans and responsiveto the amplitudes of said first and second output :pulses Yfor producing. rst .and second control voltages Varying .accordingto the strengths of. said first and secondoutput pulses, means coupled to said responsive means and producing athird. control Voltage` varyingA 'according to the relative strengths oi said first :and second control -voltagesand means coupling.`

.said third control voltage to said producing means for varying the transmission therethrougl'r during'oneof said timel intervals :to maintain .the loutput rst pulses equal yin amplitude to the output second pulses.

'7. An automatic pulse amplitude balancing.;

circuit comprising means valternately producing. a :first pulseV during, arstytime.v interval ,anda

second pulse during Va second time interval,v.saidx means includinga controllable transmissionfcirlcuit transmitting said rstand second pulses,

meansv ccnpledetdoutput of. saldi? producing means; and; alternately responsive.` to: said rst and'second-nulsesffor producing an outputcontrolling;voltage:,varyingaccordingv to. the relative strengthsci: the. and secondontput pulses, and means coupling said. output: controlling voltage to said producing means for varying the transmission therethrough, during one of said time*intervalsv suclr that; theoutput.r first pulses are. equal amplitude to. the output; second pulsesi 8i- In. al; hyperbolicnavigation receiver responsi-vef torecurrent A' pulses-V transmitted from aY masterstatonaandztd. recurrent B pulses transr 1na'.-tted.fromaslavefstatonl cachot said recurrent B .pulses arriving at; the. receiver. at.` a time delayed from f the arrival of eaclrof correspondingreeurrentiA-s pulses; Syrlhronizer means.- coupled-to theoutputiof saidreceiver and producingV of: the received second recurrent pulses, pulsef. generating, means producing recurrent output pulsesof duration lessfthan-the-duration of said received frstrecurrent pulsesirst synchroniser meansfsynchronizing the recurrent output pulses from r,said-pulse.. generating means with said receivediirst recurrent pulses, secondv synchronizer meansfresponsive'to'the coincidence-'between said received frst A recurrent y pulses and the recurrent output f pulses from said ,pulse generatingV means and vproducingeutputpulses varying` according tothe amplitude-sof said received first recurrent pulses, lterfmeans-coupled to said-second synchronizer means andproducing l.a Acontrol vvoltage from .the output pulses :varying l according to the amplitude of' said :received firstrecurrent pulses, and :means coupling. the-control voltage tosaid receiver-for controlling the receiver gaintomaintainthe amplitudeof said received nrstrecurrent pulses of :.constantwalue. y

WILBERT P. FRANTZ.

Noreferences ,.cited.. 

